In the field of passive types of infrared intrusion detectors, that is, detection being based upon receiving infrared radiation emitted by an intruder, several approaches have been taken to provide for reliable detection. It has been very common to use various types of curved mirrors, particularly concavely curved mirrors, to gather infrared radiation and focus it directly onto an infrared radiation sensor. An example of such mirror arrangement is shown in United States Pat. No. 3,703,718. In order to gain detection of a broad field and establish several sensitive regions in that field, the curved mirror is made of various segments which receive radiation from various discrete, spaced-apart sensitive areas and directly reflect the radiation onto the sensor.
A similar type of mirror arrangement, in terms of segmenting the curved mirror portion of the reflector arrangement is shown is United States Pat. No. 3,886,360. In one of the embodiments, the mirror arrangement requires three reflections before the radiation is concentrated onto the infrared radiation sensor.
Other types of multi-faceted mirrors for use in infrared radiation detectors are disclosed in United States Pat. Nos. 3,923,382 and 3,972,598. The purpose of the multi-faceted curved mirror is to gather radiation from several spaced-apart discrete fields of view and focus the radiation onto a single sensing element.
With most intrusion detectors, detection is based upon movement of the intruder through various sensitive regions such as described in United States Pat. Nos. RE. 29,082 and 4,052,716. In each instance, a concave mirror is used to directly reflect gathered radiation from a field of detection onto a detector which has an array of detection points to establish movement of the intruder across the field of detection.
Other approaches to establishing broad fields of detection, which may or may not employ optic lenses, is disclosed in United States Pat. No. 3,958,118. Movement of the intruder through the various fields of detection is needed in order to set off the alarm. In this particular instance, there is sequential directing of radiation onto the group of detectors as the body passes through the field. Such movement of sensed radiation across the detector face sets off an alarm.
In most of the above arrangements, in order to provide a broad field of detection, the unit becomes relatively large and, in some instances, of little use other than in an industrial or military application. Further, in providing a broad field of sensitive areas in intrusion detection, most of the above systems require segmenting of the curved mirror which reduces the amount of radiation which can be gathered from any one sensitive region given the constraints on total system size.
It is, therefore, an object of this invention to provide a compact, infrared radiation intrusion detector which is economical to manufacture, useful in domestic, industrial military applications and has a relatively broad multiple field of detection.